Liquid crystal display

ABSTRACT

The device includes: a write-gray scale level determining means ( 2 ), ( 3 ) for determining the write-gray scale level data for input image data that compensates the optical response characteristic of a liquid crystal display panel ( 4 ), in accordance with, at least, the combination of the gray scale level transitions from a previous vertical period to a current vertical display period; and an achievable gray scale level determining means ( 5 ), ( 6 ) for generating the achievable gray scale level data for input image data after a lapse of one vertical display period of the liquid crystal display panel, in accordance with, at least, the combination of the gray scale level transitions from one vertical display period to the next. The write-gray scale level determining means ( 2 ), ( 3 ) determines the write-gray scale level data to be supplied to the liquid crystal display panel ( 4 ), based on the achievable gray scale level data of the liquid crystal display panel ( 4 ), corresponding to the input image data at the previous vertical display period, output from the achievable gray scale level determining means ( 5 ), ( 6 ) and the input image data at the current vertical display period. In this way, it is possible to correctly inhibit generation of afterimages and present correct display of half gray scales even for motion pictures containing any kind of gray scale level transition, by implementing overshoot drive of the liquid crystal display panel using actual achievable gray scale levels within the one vertical display period, even if any type of gray scale level transition occurs from one vertical display period to the next.

TECHNICAL FIELD

The present invention relates to a liquid crystal display for displayingimages using a liquid crystal display panel and in particular relates toa liquid crystal display which offers improvement in response speed inresponse to gray scale changes in the liquid crystal display panel.

BACKGROUND ART

Recently, as personal computers and television receivers have becomelighter and thinner, reduction in thickness and weight of displaydevices has also been wanted. In answer to such demands, flat panel typedisplays such as liquid crystal displays (LCDs) have been developed inplace of cathode ray tubes (CRTs).

An LCD is a display device which produces desired image signals byapplying electric fields across a liquid crystal layer havinganisotropic dielectric constants, injected between a pair of substratesso that the strength of the electric fields is controlled to therebycontrol the amount of light passing through the substrates. Such LCDsare typical examples of handy flat panel type displays. Of these, TFTLCDs that employ thin-film transistors (TFT) as switching elements aremainly in use.

Lately, since TFT LCDs have been not only used as the display devices ofcomputers but also used widely as the display devices of televisionreceivers, the need for rendering motion pictures has been increased.However, since the conventional TFT LCDs are low in response speed, theyhave a drawback that it is difficult to reproduce motion pictures.

In order to make the liquid crystal response speed problem better, thereis a known liquid crystal driving method wherein in accordance with thecombination of the input image data of the previous frame and the inputimage data of the current frame, either a higher (overshot) drivevoltage than the predetermined gray scale level voltage that correspondsto the input image data of the current frame or a lower (undershot)drive voltage is supplied to the liquid crystal display panel. In thisspecification of the present application, this driving scheme should bedefined as overshoot drive.

FIG. 7 shows a schematic configuration of a conventional overshoot drivecircuit. Specifically, the input image data (current data) of the N-thframe being about to be displayed and the input image data (previousdata) of the (N−1)-th frame being stored in a frame memory 1 are loadedinto a write-gray scale level determining portion 2, wherein thepatterns of the gray scale level transitions between both the data andthe input image data of the N-th frame are checked with an OS tablememory (applied voltage data table) 3 stored in an external memory, sothat the write-gray scale level data needed for image display of N-thframe is determined based on the applied voltage data that is obtainedfrom the checkup, and is supplied to a liquid crystal display panel 4.

With a general liquid crystal display panel, there has been a problem inthat it takes long time to make a transition from a certain half grayscale level to another half gray scale level, so that it is impossibleto display the half gray scales within the period of one frame (e.g.,16.7 msec. for a case of progressives can of 60 Hz). This not onlyproduces afterimages but also hinders correct half gray scale display.Use of the above-described overshoot drive, however, enables display ofthe aimed half gray scales within a short time (one frame period) asshown in FIG. 8.

Here, since the above-described overshoot drive scheme is implemented onthe basis that the liquid crystal display panel is always able todisplay the target gray scale level after one frame period for every thegray scale level transition, the input image data of the previous frameis directly input as the previous data to write-gray-scale leveldetermining portion 2. However, if the liquid crystal has a poorresponse characteristic or when the data is constructed of 8 bitsrepresenting 256 gray scale levels, there has been a problem in that theresponse of the liquid crystal to the gray scale level of the currentframe image data cannot be sufficiently compensated if the gray scalelevel of the previous frame image data is zero and transits to a halfgray scale level.

To deal with this problem, for example, Japanese Patent ApplicationLaid-open Hei 7 No. 20828 proposes a liquid crystal display as shown inFIG. 9. This liquid crystal display includes: a signal processor 11 thatprocesses an input image signal Xn so as to compensate the transmittanceresponse characteristic with respect to the voltage applied to theliquid crystal; and a response predictor 12 that implements a low-passfiltering process that approximates the voltage response characteristicof the liquid crystal, on the output Zn from this signal processor 11and feeds back the output signal Yn−1 as a corresponding predicted valuefor the liquid crystal response voltage to signal processor 2.

The above response predictor 12 approximates the liquid crystal responsecharacteristic, using a set of low-pass filters (LPFs) with which thecoefficient α is varied depending on the voltage level. With thismethod, the actual liquid crystal response voltage at the previous fieldcan be approximated by the LPF output, therefore this voltage can beused as the initial voltage (previous data) at the next field so as tobe able to compensate for the liquid crystal optical responsecharacteristics in a more faithful manner.

In the case of the above-described conventional liquid crystal displaydescribed in Japanese Patent Application Laid-open Hei 7 No. 20828, theactual liquid crystal response voltage (displayed gray scale level) ofthe next field is calculated by approximating the liquid crystalresponse characteristic based on the voltage-level dependent LPF set.Nevertheless, as also understood from FIG. 10, for example, it is knownthat a typical liquid crystal display panel presents irregular responsecharacteristics depending on the combination of the gray scale levelbefore change (transition) and that after change (transition), and theresponse speed markedly lowers at transitions between particular grayscale levels.

In sum, it is impossible to obtain the exact achievable gray scalelevels after a lapse of the one vertical display period for all the grayscale level transition patterns, by approximating the liquid crystalresponse characteristic based on the voltage level dependent LPF set asdisclosed in Japanese Patent Application Laid-open Hei 7 No. 20828,hence the response and fidelity of liquid crystal to the display ofmotion pictures including half gray scales cannot be fully compensatedfor and the problem is not yet solved.

The present invention has been devised in view of the above problem toprovide a liquid crystal display which, if any type of gray scale leveltransition occurs from one vertical display period to the next, or evenif the gray scale level does not reach the aimed gray scale level withinone vertical display period, is able to correctly inhibit generation ofafterimages and present correct display of half gray scales even formotion pictures containing any kind of gray scale level transitionpattern, by implementing overshoot drive using actual achievable grayscale levels within the one vertical display period.

DISCLOSURE OF INVENTION

The first invention of this application is a liquid crystal display forimage display using a liquid crystal display panel, comprising: awrite-gray scale level determining means for determining write-grayscale level data for input image data that compensates an opticalresponse characteristic of the liquid crystal display panel, inaccordance with, at least, a combination of gray scale level transitionsfrom a previous vertical display period to a current vertical displayperiod; and an achievable gray scale level determining means forgenerating achievable gray scale level data for input image data after alapse of one vertical display period of the liquid crystal displaypanel, in accordance with, at least, a combination of gray scale leveltransitions from one vertical display period to the next, and whereinthe write-gray scale level determining means determines the write-grayscale level data to be supplied to the liquid crystal display panel,based on achievable gray scale level data of the liquid crystal displaypanel, corresponding to input image data at the previous verticaldisplay period, output from the achievable gray scale level determiningmeans and the input image data at the current vertical display period.

The second invention of this application is characterized in that theachievable gray scale level determining means, referring to a tablememory that stores achievable gray scale level parameters representingachievable gray scale brightness after the lapse of one vertical displayperiod of the liquid crystal display panel, obtained from an actualmeasurement of the optical response characteristic of the liquid crystaldisplay panel, determines the achievable gray scale level data after thelapse of one vertical display period of the liquid crystal displaypanel, in accordance with the input image data.

The third invention of this application is characterized in that thetable memory stores achievable gray scale level parameters which areaccessible by designating the achievable gray scale level data of theliquid crystal display panel corresponding to the image data at theprevious vertical display period and the input image data at the currentvertical display period.

The fourth invention of this application is characterized in that theachievable gray scale level determining means determines the achievablegray scale level data corresponding to the input image data after thelapse of one vertical display period of the liquid crystal displaypanel, using a function that represents achievable gray scale brightnessafter the lapse of one vertical display period of the liquid crystaldisplay panel, obtained from an actual measurement of the opticalresponse characteristic of the liquid crystal display panel.

The fifth invention of this application further comprises a temperaturedetecting means for detecting a device interior temperature, and ischaracterized in that the achievable gray scale level determining means,based on the detected device interior temperature, determines theachievable gray scale level data for the input image data after thelapse of one vertical display period.

The sixth invention of this application is characterized in that thewrite-gray scale level determining means, based on the detected deviceinterior temperature, determines the write-gray scale level data forcompensating the optical response characteristic of the liquid crystaldisplay panel.

In the liquid crystal display of the present invention, the achievablegray scale level data that represents the actually achievable gray scalebrightness after a lapse of one vertical display period of the liquidcrystal display panel, obtained from the input image data of theprevious vertical display period, is determined. The thus obtained datais referred to as the previous data so as to implement overshoot drivefor the input image data (current data) of the current vertical displayperiod. Therefore, this configuration enables the liquid crystal displaypanel to achieve the correct gray scale brightness designated by theinput image data after a lapse of one vertical display period, hence cancorrectly prevent occurrence of after images and correctly display halfgray scales for any motion picture whatever gray scale transitions itcontains.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a functional block diagram showing the schematic exemplaryconfiguration of the first embodiment of a liquid crystal display of thepresent invention.

FIG. 2 is an illustrative chart showing the step response characteristicof a liquid crystal display panel for a certain gray scale leveltransition pattern.

FIG. 3 is a schematic illustrative chart showing a content example of anOS table in the first embodiment of the liquid crystal display of thepresent invention.

FIG. 4 is a functional block diagram showing the schematic exemplaryconfiguration of the second embodiment of a liquid crystal display ofthe present invention.

FIG. 5 is a functional block diagram showing the schematic exemplaryconfiguration of the third embodiment of a liquid crystal display of thepresent invention.

FIG. 6 is an illustrative chart showing an example of relations betweenthe device interior temperature and reference table memories in thethird embodiment of the liquid crystal display of the present invention.

FIG. 7 is a functional block diagram showing the schematic exemplaryconfiguration of a conventional liquid crystal display.

FIG. 8 is an illustrative chart showing the relations between thevoltage applied to liquid crystal and the liquid crystal response.

FIG. 9 is a functional block diagram showing the schematic exemplaryconfiguration of another conventional liquid crystal display.

FIG. 10 is an illustrative chart showing the relations between grayscale level transitions and response times of a liquid crystal displaypanel.

BEST MODE FOR CARRYING OUT THE INVENTION

The first embodiment of a liquid crystal display of the presentinvention will hereinbelow be described in detail with reference toFIGS. 1 to 3. The same reference numerals are allotted to the samecomponents as in the above conventional example without description.Here, FIG. 1 is a block diagram showing the schematic exemplaryconfiguration of the liquid crystal display of this embodiment; FIG. 2is an illustrative chart showing the step response characteristic of aliquid crystal display panel for a certain gray scale level transitionpattern; and FIG. 3 is a schematic illustrative chart showing a contentexample of an OS table in the liquid crystal display of this embodiment.

The liquid crystal display of this embodiment includes: an achievablegray scale level determining portion 5 which, as shown in FIG. 1,receives the output (previous data) from a frame memory 1 and the inputimage data (current data), determines the achievable gray scale leveldata corresponding to the input image data, after a lapse of one frameperiod (16.7 msec), which is obtained from the optical responsecharacteristic of a liquid crystal display panel 4 with reference to anachievable gray scale level table memory (ROM) 6, and outputs the resultto frame memory 1. Here, it goes without saying that the one frameperiod of the input image data is not limited to 16.7 msec as long asthe input image data is sequentially scanned data.

A write-gray scale level determining portion 2 acquires the achievablegray scale level data of liquid crystal display panel 4 corresponding tothe input image data of the previous frame stored in frame memory 1 asthe previous data, and determines the write-gray scale level data thatwill compensate the optical response characteristic of liquid crystaldisplay panel 4, in accordance with the combination of the gray scalelevel transitions from the previous data to the input image data of thecurrent frame (current data). In other words, the write-gray scale leveldata which enables liquid crystal display panel 4 to display, after oneframe period (16.7 msec), the correct brightness of the gray scalesdetermined by the image data of the current frame, is determined andthis is supplied to liquid crystal display panel 4.

In the case where, for example, overshoot drive is implemented for aliquid crystal display panel having a step response characteristic shownin FIG. 2, if a target gray scale level #A, which is designated by theimage data, cannot be achieved within one frame period (16.7 msec), theabove-described conventional configuration with reference to FIG. 7,determines the write-gray scale level data for the liquid crystal toachieve the target gray scale level #B, designated by the current frameimage data (current data), after a lapse of one frame period, byreferring to the target gray scale level #A that is determined as theprevious data by the previous frame image data. In contrast, the presentembodiment, referring to the actual achievable gray scale level after alapse of one frame period, #A′, as the previous data, determines thewrite-gray scale level data for the liquid crystal to achieve the targetgray scale level #B, designated by the current frame image data (currentdata), after a lapse of one frame period.

That is, even if the liquid crystal display panel cannot achieve thetarget gray scale level #A, which is designated by the image data of theprevious frame, within one frame period, due to the above-mentionedvarious causes, in the present embodiment the amount of overshoot(write-gray scale level data) for the current frame image data isdetermined using the actual achievable gray scale level #A′. Therefore,it is possible to enable the liquid crystal display panel to make thecorrect response after a lapse of one frame period, achieving the targetgray scale level #B designated by the current frame image data.

In liquid crystal display panel 4, the gray scale level drive voltagecorresponding to the write-gray scale level data determined bywrite-gray scale level determining portion 2 is applied to the liquidcrystal layer to display a desired image. Here, in the presentembodiment, write-gray scale level determining portion 2 with an OStable memory 3 constitutes a write-gray scale level determining means,and achievable gray scale level determining portion 5 with an achievablegray scale level table memory 6 constitutes an achievable gray scalelevel determining means.

In this case, when the number of display signal levels, i.e., the amountof display data, is 256 gray scales represented by 8 bits, all pieces ofwrite-gray scale level data (the amounts of overshoot) for all the grayscale level transition patterns are stored in a 256×256 matrix, in OStable memory (ROM) 3, as shown in FIG. 3. These amounts of overshootstored in this OS table memory 3 are obtained from the actualmeasurement of the optical response characteristic of the liquid crystaldisplay panel 4 used for the device, each value being determined inaccordance with the combination of the gray scale level of the currentframe image data and the gray scale level of the previous frame imagedata.

In achievable gray scale level table memory (ROM) 6, the achievable grayscale level data in liquid crystal display panel 4 after a lapse of oneframe period (16.7 msec), obtained for every combination of the grayscale level transitions from one frame to the next, depending on theinput image data (current data), is stored in a 256×256 matrix, in asimilar manner to that of the OS table memory 3 shown in FIG. 3. Thesevalues are determined based on the actual measurement of the opticalresponse characteristic of the liquid crystal display panel 4 used forthe device, i.e., the actual achievable gray scale brightness in liquidcrystal display panel 4 after a lapse of one frame period, measured forevery gray scale level transition pattern.

In the above-described OS table memory 3 and achievable gray scale leveltable memory 6, all pieces of the write-gray scale level data andachievable gray scale level data for the 256×256 grayscale leveltransition patterns are stored. However, it is also possible that onlythe transition parameters (actual measurements) at representative points(representative gray scale level transition patterns) distributed evenlyor unevenly have been stored so that the values for the other gray scalelevel transition patterns can be calculated from the above conversionparameters (actual measurements).

For example, only the conversion parameters (actual measurements) forrepresentative gray scale level transitions for every 64 gray scalelevels, have been stored in a 5×5 matrix, so that, for the other grayscale level transition patterns, the write-gray scale level data (theamounts of overshoot) that compensates the optical responsecharacteristic of liquid crystal display panel 4 and the achievable grayscale level data corresponding to the gray scale brightness actuallyachieved by liquid crystal display panel 4 after a lapse of one frameperiod can be determined by implementing linear interpolation or othercalculations on the above conversion parameters (actual measurements).

Since the liquid crystal display panel of the present embodiment is thusconfigured, the achievable gray scale level data corresponding to thegray scale levels achieved based on the previous frame input image databy liquid crystal display panel 4 after a lapse of one frame period, canbe stored as the previous data in frame memory 1 for any input imagewhatever gray scale transitions it includes. The achievable gray scaledata is that based on the actual measurement (gray scale brightness) inliquid crystal display panel 4 of the present device, and contains allthe gray scale transition patterns. Therefore, it is possible to obtaincorrect previous data in conformity with the optical responsecharacteristic of the actual liquid crystal display panel 4.

The write-gray scale level determining portion 2, based on theachievable gray scale level data of liquid crystal display panel 4corresponding to the previous frame input image data output from framememory 1 and the current frame input image data, determines thewrite-gray scale level data for the liquid crystal display panel 4 to beable to achieve the gray scale brightness designated by the currentframe input image data, after a lapse of one frame period. Therefore, itis possible to implement an overshoot drive which can prevent occurrenceof afterimages and can correctly display the half gray scales bycorrectly compensating for the optical response characteristic of theliquid crystal display panel 4 for any motion picture whatever grayscale transitions it contains.

Next, the second embodiment of a liquid crystal display of the presentinvention will be described in detail with reference to FIG. 4. The samecomponents as described in the above first embodiment are allotted withthe same reference numerals without description. FIG. 4 is a blockdiagram showing a schematic exemplary configuration of the liquidcrystal display of the present embodiment.

The optical response characteristic of a liquid crystal panel 4 variesdepending on the alignment mode of the liquid crystal, the electrodestructure for applying electric fields to the liquid crystal material,and other factors. The liquid crystal display of this embodimentincludes, in place of achievable gray scale level table memory 6 of theabove first embodiment, a calculator 7 for implementing calculation of a2-dimentional function f(pre, cur), which is defined by variables, orthe gray scale level before transition and the gray scale level aftertransition and represents the optical response characteristic of theliquid crystal display panel 4, as shown in FIG. 4. This 2-dimentionalfunction f (pre, cur) is a function representing the achievable grayscale brightness of the liquid crystal display panel 4 after a lapse ofone frame period, which is determined by actual measurement of theoptical response characteristic of liquid crystal display panel 4.

An achievable gray scale level determining portion 5, based on thecalculation of the 2-dimentional function (pre, cur) from the calculator7, determines the actual achievable gray scale level data of the liquidcrystal display panel after a lapse of one frame period for the inputimage data (current data), and outputs it as the previous data to aframe memory 1. In sum, in the present embodiment achievable gray scalelevel determining portion 5 and calculator 7 constitute the achievablegray scale level determining means.

Accordingly, similar to the above first embodiment which uses achievablegray scale level table 6 containing the achievable gray scale levelparameters obtained from the actual measurement of the achievable grayscale brightness of liquid crystal panel 4 after a lapse of one frameperiod, the achievable gray scale level data corresponding to the grayscale brightness levels achieved based on the previous frame input imagedata by liquid crystal display panel 4 after a lapse of one frameperiod, can be stored as the previous data in frame memory 1 for anyinput image whatever gray scale transitions it includes. Therefore, itis possible to obtain correct previous data in conformity with theoptical response characteristic of the actual liquid crystal displaypanel 4.

The write-gray scale level determining portion 2, based on theachievable gray scale level data of liquid crystal display panel 4corresponding to the previous frame input image data output from framememory 1 and the current frame input image data, determines thewrite-gray scale level data for the liquid crystal display panel 4 to beable to achieve the gray scale brightness designated by the currentframe input image data, after a lapse of one frame period. Therefore, itis possible to implement an overshoot drive which can correctly preventoccurrence of afterimages and can correctly display the half gray scalesby making up for the optical response characteristic of the liquidcrystal display panel 4 for any motion picture whatever gray scaletransitions it contains.

Next, the third embodiment of a liquid crystal display of the presentinvention will be described in detail with reference to FIGS. 5 and 6.The same components as described in the above first embodiment areallotted with the same reference numerals without description. Here,FIG. 5 is a block diagram showing the schematic exemplary configurationof the liquid crystal display of the present embodiment. FIG. 6 is anillustrative chart showing an example of relations between the deviceinterior temperature and reference table memories in the liquid crystaldisplay of the present embodiment.

It is known that the response-speed of liquid crystal greatly depends ontemperature, in particular, the input signal following performance atlow temperatures lowers extremely and the response time increases. Thismeans that the gray scale brightness of the liquid crystal display panelin accordance with the input image data after a lapse of one frameperiod changes also depending on the temperature of the liquid crystaldisplay panel.

To deal with this, the liquid crystal display of the present embodiment,as shown in FIG. 5, includes: OS table memories (ROM) 3 a to 3 c thatstore OS parameters for a plurality of device interior temperatures;achievable gray scale level table memories (ROM) 6 a to 6 c storingachievable gray scale level parameters for the plurality of deviceinterior temperatures; a temperature sensor 8 for detecting thetemperature inside the device; and a control CPU 9 for selecting onefrom OS table memories 3 a to 3 c and one from achievable gray scalelevel table memories 6 a to 6 c, in accordance with the device interiortemperature, detected by the temperature sensor 8.

Here, OS parameters LEVEL1 to LEVEL3 stored in OS table memories 3 a to3 c should be obtained beforehand from the actual measurements of theoptical response characteristic of liquid crystal display panel 4 underenvironments at reference temperatures T1, T2 and T3 (T1<T2<T3).Similarly, achievable gray scale level parameters LEVEL1 to LEVEL3stored in achievable gray scale level table memories 6 a to 6 c shouldbe obtained beforehand from the measurements of the optical responsecharacteristic of liquid crystal display panel 4 under environments atreference temperatures T1, T2 and T3 (T1<T2<T3).

Control CPU 9 compares the detected temperature data from temperaturesensor 8 with predetermined threshold temperature data values Th1 andTh2 and based on the comparison, generates and outputs a switchingcontrol signal that selects one of OS table memories 3 a to 3 c forswitching to any of OS parameter LEVEL1 to LEVEL3 and selects one ofachievable gray scale level OS table memory 6 a to 6 c for switching toany of achievable gray scale level parameter LEVEL1 to LEVEL3.

It should be noted that temperature sensor 8 is preferably disposed at aposition so as to detect the temperature of liquid crystal display panel4, and one or more sensors may be arranged at different positions insidethe device.

In this case, if the device interior temperature detected fromtemperature sensor 8 is not higher than the threshold temperature Th1(=10° C.), control CUP 9 gives write-gray scale level determiningportion 2 a command of selecting OS table memory 3 a and referring toit, as shown in FIG. 6, for example. In answer to this, write-gray scalelevel determining portion 2 determines the write-gray scale level datacorresponding to the input image data, in accordance with the gray scalelevel transitions from the previous frame to the current frame, usingthe OS parameter LEVEL1 stored in OS table memory 3 a, and provides theobtained result to liquid crystal display panel 4.

At the same time, control CPU 9 gives achievable gray scale leveldetermining portion 5 a command for selecting and referring toachievable gray scale level table memory 6 a. In answer to this,achievable gray scale level determining portion 5 determines theachievable gray scale level data corresponding to the input image data,in accordance with the gray scale level transitions from the previousframe to the current frame, using the achievable gray scale levelparameter LEVEL1 stored in achievable gray scale level table memory 6 a,and provides the obtained result to frame memory 1.

When the device interior temperature detected from temperature sensor 8is higher than the threshold temperature Th1 (=10° C.) and not higherthan the threshold temperature Th2 (=30° C.), control CPU 9 giveswrite-gray scale level determining portion 2 a command for selecting OStable memory 3 b and referring to it. In answer to this, write-grayscale level determining portion 2 determines the write-gray scale leveldata corresponding to the input image data, in accordance with the grayscale level transitions from the previous frame to the current frame,using the OS parameter LEVEL2 stored in OS table memory 3 b, andprovides the obtained result to liquid crystal display panel 4.

At the same time, control CPU 9 gives achievable gray scale leveldetermining portion 5 a command for selecting and referring toachievable gray scale level table memory 6 b. In answer to this,achievable gray scale level determining portion 5 determines theachievable gray scale level data corresponding to the input image data,in accordance with the gray scale level transitions from the previousframe to the current frame, using the achievable gray scale levelparameter LEVEL2 stored in achievable gray scale level table memory 6 b,and provides the obtained result to frame memory 1.

Further, when the device interior temperature detected from temperaturesensor 8 is higher than the threshold temperature Th2 (=30° C.), controlCPU 9 gives write-gray scale level determining portion 2 a command forselecting OS table memory 3 c and referring thereto. In answer to this,write-gray scale level determining portion 2 determines the write-grayscale level data corresponding to the input image data, in accordancewith the gray scale level transitions from the previous frame to thecurrent frame, using the OS parameter LEVEL3 stored in OS table memory 3c, and provides the obtained result to liquid crystal display panel 4.

At the same time, control CPU 9 gives achievable gray scale leveldetermining portion 5 a command for selecting and referring toachievable gray scale level table memory 6 c. In answer to this,achievable gray scale level determining portion 5 determines theachievable gray scale level data corresponding to the input image data,in accordance with the gray scale level transitions from the previousframe to the current frame, using the achievable gray scale levelparameter LEVEL3 stored in achievable gray scale level table memory 6 c,and provides the obtained result to frame memory 1.

As has been described heretofore, according to the liquid crystaldisplay of the present embodiment, one of achievable 10, gray scalelevel table memories 6 a to 6 c is selectively referred to in accordancewith the device interior temperature. Therefore, it is always possibleto determine correct achievable gray scale level data of liquid crystaldisplay panel 4 and store the data into frame memory 1 as the previousdata. Thus, it is possible to obtain correct previous data that conformsto the optical response characteristic of the actual liquid crystaldisplay panel 4 presenting temperature-dependence.

Also, write-gray scale level determining portion 2, selectivelyreferring to one of OS table memories 3 a to 3 c in accordance with thedevice interior temperature, determines the write-gray scale level datathat can achieve the gray scale brightness designated by the currentframe input image after a lapse of one frame period, based on theachievable gray scale level data of liquid crystal display panel 4corresponding to the input image data for the previous frame, outputfrom frame memory 1, and the current frame input image data. Therefore,it is possible to implement an overshoot drive which can correctlyprevent occurrence of afterimages and can correctly display the halfgray scales by always making up for the optical response characteristicof liquid crystal display panel 4 for any motion picture whatever grayscale transitions it contains.

In the above embodiment, three kinds of OS table memories 3 a to 3 c andachievable gray scale level table memories 6 a to 6 c, respectivelycorresponding to three levels of temperature ranges (below 10° C., 10°C. to 30° C. and above 30° C.), are provided, one of OS table memories 3a to 3 c as well as one of achievable gray scale level table memories 6a to 6 c is selectively referred to in accordance with the detected dataof the device interior temperature. However, it goes without saying thatOS table memories and achievable gray scale level table memories for twolevels or four or more levels of temperature ranges may be provided.

Also, instead of providing table memories corresponding to a pluralityof levels of temperature, the write-gray scale level data (the amountsof overshoot) for compensating the optical response characteristic ofliquid crystal display panel 4 as well as the achievable gray scalelevel data corresponding to the gray scale brightness actually achievedby the liquid crystal display panel after a lapse of one frame period,may be determined by implementing a predetermined operation inaccordance with the device interior temperature, on the conversionparameters stored in a single table memory.

Further, in the embodiment of the present invention, the response speedof the liquid crystal display panel is improved by comparing theprevious frame image data and the current frame image data anddetermining, based on the comparison result, the write-gray scale leveldata corresponding to the current frame image data. However, it is ofcourse possible to provide a configuration in which the write-gray scalelevel data for compensating the optical response characteristic of theliquid crystal display pane is determined based on the image data two,three or more frames before, for example.

Similarly, it is also possible to provide a configuration in which theachievable gray scale level data, corresponding to the current imagedata after a lapse of one frame period, in the liquid crystal displaypanel, may be determined using the image data (achievable gray scalelevel data) two, three, or more frames before in addition to theprevious image data (achievable gray scale level data) and current frameimage data.

Since the liquid crystal display of the present invention is thusconfigured as above, even if the target gray scale level is not achievedwithin one vertical display period, the liquid crystal display panel iscontrolled by overshoot drive based on the achievable gray scale level(the achievable gray scale level based on the actual measurement of thegray scale brightness of the liquid crystal display panel), whereby itis possible to prevent occurrence of afterimages and correctly displaythe half gray scales for any motion picture whatever gray scaletransitions it contains, by making up for the optical responsecharacteristic of the liquid crystal display panel.

Industrial Applicability

The liquid crystal display according to the present invention issuitable for use in display devices for personal computers, televisionreceivers, wherein the optical response characteristic of a liquidcrystal display panel for gray scale level transitions is compensated byimplementing overshoot drive in the liquid crystal display panel.

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 5. A liquidcrystal display for image display using a liquid crystal display panel,comprising: a write-gray scale level determining section for determiningwrite-gray scale level data for input image data that compensates anoptical response characteristic of the liquid crystal display panel, inaccordance with, at least, a combination of gray scale level transitionsfrom a previous vertical display period to a current vertical displayperiod; an achievable gray scale level determining section forgenerating achievable gray scale level data for input image data after alapse of one vertical display period of the liquid crystal displaypanel, in accordance with, at least, a combination of gray scale leveltransitions from one vertical display period to the next; and atemperature detector for detecting a device interior temperature,wherein the write-gray scale level determining section determines thewrite-gray scale level data to be supplied to the liquid crystal displaypanel, based on achievable gray scale level data of the liquid crystaldisplay panel, corresponding to input image data at the previousvertical display period, output from the achievable gray scale leveldetermining section and the input image data at the current verticaldisplay period, and wherein the achievable gray scale level determiningsection, based on the detected device interior temperature, determinesthe achievable gray scale level data for the input image data after thelapse of one vertical display period of the liquid crystal displaypanel.
 6. The liquid crystal display according to claim 5, wherein thewrite-gray scale level determining section, based on the detected deviceinterior temperature, determines the write-gray scale level data forcompensating the optical response characteristic of the liquid crystaldisplay panel.